The concept of a "color cube" or "color solid" for representing color in three dimensions is well known. In a color cube three different primary colorants are combined in various amounts and proportions with a base color, such as black or white, to yield a spectrum of colors. The color cube is arranged so that the three selected primary colors, such as cyan, magenta and yellow, are arranged along three mutually perpendicular and intersecting edges of the cube. The cube corner where the three primary colorant edges merge is taken as the base point, and the amount of each primary will vary from a minimum at this base corner to a maximum at the opposite end of the respective edge.
The color variation will normally be uniform along each edge of the cube so that each face of the cube will represent the spectrum of colors reproducible when one of the primaries is held constant in either its minimum or maximum amount and the other two primaries are varied. Points which lie within the color cube represent colors obtained by combining various proportions of all three of the primary colors with the base color. For example, the diagonal axis joining the opposite white and black corners of the cube represents shades of grey which may be derived from combining equal amounts of the three primary colours with either white or black.
Heretofore, the colour cube concept has been used as a theoretical model for understanding colour and as a basis for constructing two dimensional color chart systems. Such color chart systems typically comprise an ordered array of two dimensional charts which represent various subsets of the color cube. For example, two dimensional charts may be derived by passing a series of vertical or horizontal planes through the color cube at various locations. Such two dimensional charts are of considerable value to printers and the like who are frequently called upon to identify, match and duplicate colors and to choose complimentary and contrasting colors.
In addition to developing color chart systems based on parallel, vertical or horizontal sections through a theoretical color cube, more sophisticated color charts may be derived by logically dissecting a color cube along a series of planes perpendicular to a diagonal axis of the cube, as is described in U.S. Pat. No. 4,009,527 Scott et al. issued 1 Mar., 1977. The advantage of the Scott system is that all three of the primary colorants are varied on each of the sequential color charts. Thus all three of the primary colorants change simultaneously as one moves from chart to chart in sequence, and the consecutive charts offer progressively increasing color densities.
U.S. Pat. No. 3,751,829 Foss issued 14 Aug. 1973, also discloses a series of color charts based on the color cube concept. The Foss color charts are derived by logically dividing the color cube into a series of concentric and similarly oriented cubic volumes. The charts may be arranged in a variety of ways to provide a continuous two dimensional representation of the set of colors reproducible from combining the primary colorants in different amounts and proportions.
Although such color chart systems are superior to conventional color chips and color wheels available at paint stores and the like, they do not enable a user to intuitively understand color theory or easily work with color in three dimensions. In order to be fully effective, a color chart or model should preferably embody all of the following characteristics:
(1) The model should represent the entire set of colors reproducible in a given medium. Such colors should be arranged in an ordered fashion so that they may be conveniently accessed and visually compared without iteratively flipping from chart to chart. PA1 (2) The model should provide a system for meaningfully describing every color within the color set. PA1 (3) The model should indicate how to reproduce a selected color in the given medium by combining one or more primary colors and base color for that medium. PA1 (4) The model should facilitate mapping of a selected color from one medium (such as a computer color monitor) to another medium (such as a photographic slide).
Although conventional two dimensional color chart systems are useful for many purposes, they are not capable of satisfying all of the above requirements. The need has therefore arisen for a three dimensional physical model based on the color cube concept which may be employed as a tool for choosing colors, describing colors, reproducing colors, and mapping colors between different color media.